The present invention relates to an arrangement and a corresponding method and computer system for estimating the input torque of a dual-clutch transmission for a vehicle, said transmission comprising an inner input shaft and an outer input shaft being arranged concentrically with respect to said inner input shaft, said arrangement further comprising a dual-clutch assembly connecting said shafts to an output shaft of an engine.
In the field of heavy transport vehicles, it is known that such a vehicle can be provided with a transmission unit of the kind which is provided with a dual clutch. According to known technology, a dual-clutch transmission is based on the principle that two single-plate or multi-plate clutches are used for operating a number of gears. For example, the two clutches can be arranged concentrically, in a manner so that an outer clutch drives the odd-numbered gears whereas an inner clutch drives the even-numbered gears of the transmission.
Shifting between gears in the dual-clutch transmission can be accomplished by applying torque from the vehicles engine to one of the two clutches while the torque is being disconnected from the other clutch. In this manner, shifting between gears can be carried out generally without interrupting, the torque being transferred to the driven road wheels. Also, shifting can be carried out more quickly than in transmissions of the single-clutch type.
As previously known, a dual-clutch transmission can be arranged with two input shafts, each one being connected to a friction clutch and also to the output of the vehicle engine. Functionally, this is equivalent to having two conventional transmissions in parallel, that is two parallel sub-transmissions, and using one at a time for power transfer. Suitably, the two input shafts are arranged in a concentrical manner, i.e. so that a first input shaft constitutes an inner input shaft which extends inside an outer input shaft.
The sub-transmission that is not used, thus idling for the time being, can have a gear engaged and prepared for a subsequent shift. This shift is carried out by simultaneously disengaging the friction clutch of the previously used sub-transmission and engaging the friction clutch of the previously idling sub-transmission.
In order to operate a dual-clutch transmission in an optimal manner, there is a need for control of the transmission by means of a computerized transmission control unit. Such a unit uses signals from a number of sensors, and also input from an engine control unit, in order to determine the timing of changing gears and other parameters which affect the shilling operation. This process is optimized in order to obtain, for example, a high level of performance, fuel economy and vehicle handling.
In order to optimize the gear-changing process in a dual-clutch transmission, an input signal indicating the input torque acting upon the two input shafts is required. A conventional torque sensor is a component which is costly and which is also a relatively large component which is difficult to fit within a transmission unit. For this reason, an alternative solution is to estimate the torque—i.e. instead of actually measuring the torque—based on certain parameters such as the amount of fuel injected to the vehicle engine, the engine speed, the temperature and other parameters. This gives an estimate of the input torque which is sufficiently accurate in order to operate transmission in a suitable manner.
A signal representing a directly sensed input torque acting upon the transmission enables a number of functions to be implemented, such as for example a feedback control of the transmitted torque in the clutch of the transmission; a clutch diagnosis; engine diagnosis; and improved robustness of transmission control (with regard to gear shifting, gear selection etc).
In summary, in a dual-clutch transmission for vehicles, two concentrically arranged input shafts are utilized. In order to control the transmission in an optimal manner, a signal representing the input torque acting upon each of the input shafts can be provided by means of a torque sensor. Alternatively, an estimate of the torque can be determined based upon certain parameters.
Implementing a torque sensor on a traditional single input-shaft transmission is straightforward. However, for a transmission with dual concentric input shafts it is very difficult to measure the torque on the inner input shaft. This is mainly clue to the difficulty of mounting the sensor on the inner input shaft, i.e. inside the outer input shaft. Currently available solutions will be too expensive or will have poor accuracy.
EP2272729 discloses an example of prior art comprising a dual-clutch transmission with a torque sensor 22 arranged on one of the two input shafts of the dual-clutch transmission.
DE102008026509 discloses a method for how to via a measurement determine or estimate a torque of a shaft in a transmission without using a torque sensor.
It is previously known to use an estimated torque as described above. However, such a known method does not have the required resolution of accuracy for many of the desired functions, e.g. engine diagnosis. Consequently, a problem which exists with regard to previously known solutions is that known principles for estimating the torque are not sufficiently accurate. Also, it is not possible to use arrangement involving two separate sensors, i.e. one sensor on each inner shaft.
A problem with prior art is consequently that it does not offer any solution of providing an accurate sensor-based measurement of the torque acting upon the two input shafts of a dual-clutch transmission for a heavy transport vehicle.
Consequently, it is desirable to solve the above-mentioned problem and to provide an arrangement and method for estimating the input torque of a dual-clutch transmission in which accurate values of the input torque acting upon the input shafts of a dual-clutch transmission can be obtained in a reliable and cost-effective manner.
In accordance with an aspect of the invention, an arrangement for estimating the input torque of a dual-clutch transmission for a vehicle is provided, said transmission comprising an inner input shaft and an outer input shaft being arranged concentrically with respect to said inner input shaft, said arrangement further comprising a dual-clutch assembly connecting said shafts to an output shaft of an engine. The invention comprises a torque sensor arranged on said outer input shaft and connected to a transmission control unit; said arrangement being arranged for providing, by means of said torque sensor, a measured torque value during operation of said outer input shaft and for providing at estimated torque value during operation of said inner input shaft.
By means of an aspect of the invention, a method for achieving an accurate estimate of the inner input shaft torque is obtained, using a torque sensor that only measures the torque on the outer input shaft and using an estimated torque value during operation of the inner input shaft.
In this manner, a number of functions relating to control of the transmission and diagnosis of the engine can be implementable on a dual input shaft transmission, using only one torque sensor.
According to an embodiment, the invention is arranged so that the transmission control unit is arranged for calculating the estimated torque value by means of an observer function which is activated during said operation of the outer input shaft. The observer function is for example in the form of a Kalman filter, but the invention is not limited to such a function only.
Also, according to an embodiment, the torque sensor is also connected to an engine control unit. Suitably, the engine control unit is arranged for providing a diagnosis of the operating of said engine.
The invention also relates to a method for estimating the input torque of a dual-clutch transmission for a vehicle, wherein said transmission comprises an inner input shaft and an outer input shaft being arranged concentrically with respect to said inner input shaft, and wherein said shafts are connected to an output shaft of an engine via a dual-clutch assembly. According to this aspect of the invention, the method comprises: providing a torque sensor on said outer input shaft; connecting said torque sensor to a transmission control unit; providing, by means of said torque sensor, a value corresponding to a measured torque value when transmitting engine output torque only through said outer input shaft; and providing a value corresponding to an estimated torque value when transmitting engine output torque only through said inner input shaft.